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Dec 12, 2010 at 16:15 comment added Bill Johnson But studying a Banach space involves understanding the structure of its subspaces. 'Course the corollary to the universality of $C[0,1]$ is that we will never understand the structure of $C[0,1]$ as a Banach space.
Dec 12, 2010 at 6:35 comment added Adam Hughes I also agree, if you consider the Sobolev spaces and in particular the Hilbert-Sobolev spaces, they embed nicely into other spaces and by infinite dimensionality and separability the latter are isometrically isomorphic to $\ell^2$, but at the same time the ways to go between them isn't really easy to recover the structure of one from the other, especially trying to figure out $H^k=W^{k,2}$ from just knowledge of $\ell^2$.
Dec 12, 2010 at 3:35 comment added Peter LeFanu Lumsdaine What @fedja said. I don’t think “all widgets embed into $X$” together with “widgets are a field of study” makes $X$ a field of study. This is the same sort of argument by which a few logicians, set theorists, category theorists, etc. (and, more often, students meeting these subjects for the first time) claim “logic (set theory, category theory) subsumes all other mathematics”.
Dec 12, 2010 at 2:52 history made wiki Post Made Community Wiki by Kim Morrison
Dec 12, 2010 at 2:06 comment added fedja Be reasonable! I also was tempted to post an answer starting with "Almost anything would really do (with reasonable interpretation). An analytic function/the unit disk; A convex set/the simplex in high dimension; A graph/$\mathbb Z^3$" and ending with "And that's definitely a community wiki type question, if it is a question at all, which I have strong doubts about. Even if you had asked for "a single proof of a single statement about a single object", you would be in almost equally bad shape", but then decided to find some criterion for a good answer here instead (not that I succeeded :().
Dec 11, 2010 at 23:33 history answered Bill Johnson CC BY-SA 2.5